1. Field of the Invention
The present invention relates to packaging of semiconductor devices, such as memory devices, in stacked, three-dimensional assemblies, and especially to high-density and ultra-high-density packaging; and more particularly to such assemblies which use resilient, microelectronic spring contacts as contact elements.
2. Description of Related Art
Semiconductor devices, such as memory chips, are frequently assembled into modules such as Single Inline Memory Modules (SIMM""s), and similar assemblies. However, as electronic devices have become increasingly compact, while at the same time requiring increasing amounts of memory, SIMM""s and similar assemblies are increasingly considered too bulky for many applications. Additionally, each semiconductor device on SIMM""s and similar assemblies is integrated with its module using a relatively permanent (not readily demountable) connection method, and is not provided with connection elements that can be used both during wafer-level testing and during final assembly. Various three-dimensional, stacked assemblies of semiconductor devices have also been developed, and some of these assemblies are less bulky than SIMM""s and similar assemblies. However, many of such prior stacked assemblies suffer from the other deficiencies of SIMM""s noted above, and additional deficiencies such as being complex and expensive to manufacture, and being difficult to cool.
Commonly owned U.S. Pat. No. 5,998,864 discloses bare semiconductor devices stacked atop one another, which are offset in at least one direction so that an edge portion of each successive device in the stack extends beyond every device beneath it. Elongate contact elements extend from the bottommost device, and from the exposed edge portion of each of the remaining semiconductor devices in the stack, and connect with electrical terminals of a common stacking substrate. The stack makes use of elongate contact elements as disclosed, for example, in commonly owned U.S. Pat. No. 5,476,211 (Khandros), which are suitable for use during wafer-level burn-in and during final assembly. The assembly is highly compact, and readily fabricated at die scale. However, certain alternative structures are desirable, as further described herein.
Commonly owned, co-pending patent application Ser. No. 09/710,539, filed Nov. 9, 2000, entitled xe2x80x9cLITHOGRAPHIC SCALE MICROELECTRONIC SPRING STRUCTURES WITH IMPROVED CONTOURS,xe2x80x9d and related commonly owned, co-pending application Ser. No. 09/364,788, filed Jul. 30, 1999, entitled xe2x80x9cINTERCONNECT ASSEMBLIES AND METHODS,xe2x80x9d which applications are incorporated herein, in their entirety, by reference, disclose microelectronic spring contacts which are readily mass-produced at very fine pitches directly on terminals of semiconductor devices, such as dice and wafers, and on similar-scale substrates such as lead frames and connectors. Because of their fine pitch, low cost, and electrical performance, these microelectronic spring contacts are particularly advantageous for use in applications where a readily demountable, reusable electrical connection at a very compact scale is desired. In particular, such microelectronic spring contacts can serve as contacts both during a wafer-level device burn-in process, and during subsequent assembly of devices into a multi-component module.
There is a need, therefore, to take better advantage of microelectronic spring contacts such as described in the incorporated references in a compact and modular assembly of stacked semiconductor devices, such as a memory module. Additionally, there is a need to provide such an assembly with components for providing electrical termination and/or decoupling to a plurality of parallel semiconductor devices, for providing internal ground planes and/or power planes for controlled impedance signal traces, and for cooling the assembly. Such an assembly should be much more compact than SIMM""s and similar assemblies, and more readily and cost-effectively manufactured, assembled, and/or repaired than three-dimensional stacked assemblies according to the prior art.
The present invention provides a three-dimensional, stacked semiconductor device assembly with microelectronic spring contacts, and components thereof, that overcomes the limitations of prior art stacked assemblies and other modular assemblies, such as SIMM""s. The assembly comprises a plurality of stacked modules, which are capable of being readily mounted to, and demounted from, one another. Each module of the assembly comprises a semiconductor device, comprising a die (which may be a thinned die), mounted to a stacking substrate. The die and the stacking substrate are also capable of being readily mounted to, and demounted from one another, if desired. Any number of modules may be stacked according to the invention, limited only by the circuit configuration of the incorporated semiconductor devices. The bottommost module in the assembly is suitable for attaching directly to a substrate or other component, such as a printed circuit board, and the topmost module in the assembly preferably comprises a decoupling and/or termination substrate. The assembly may be held together using a relatively permanent method, such as by placing a suitable solder, adhesive, or other joining material between each module of the assembly. In the alternative, the assembly may be held together using a relatively demountable method, such as a compression frame and demountable mechanical fasteners; or by some combination of demountable and permanent methods.
Each semiconductor device in the assembly has terminals on a surface thereof, at least selected ones of which are provided with a contact element. In addition, each device preferably comprises one or more stop structures for the microelectronic springs on its terminal surface. Each contact element on the semiconductor device preferably comprises a microelectronic lithographic-type molded spring contact as further described in the incorporated references identified above. In the alternative, each contact element on the device comprises a contact pad or solder bump.
Each stacking substrate comprises a first mounting face, having a plurality of first contact elements disposed thereon, and a second mounting face, having plurality of second contact elements disposed thereon for contacting the first contact elements. In a preferred embodiment of the invention, the first contact elements comprise molded integral resilient free-standing microelectronic spring contacts as further described in the incorporated references identified above, and the second contact elements comprise contact pads. Each stacking substrate additionally comprises a semiconductor device mounting face, having a plurality of third contact elements disposed thereon. The device mounting face is preferably recessed below one of the first mounting face or the second mounting face. The third contact elements are configured for contacting corresponding contact elements on the semiconductor device. For example, in an embodiment of the invention, the contact elements on the semiconductor device comprise microelectronic spring contacts, and the third contact elements comprise contact pads. Where present on the stacking substrate, the microelectronic spring contacts are preferably provided with one or more stop structures, an exposed face (or faces) of which contacts an adjacent stacking substrate and/or semiconductor device. Each stacking substrate additionally includes a conductive trace between individual ones of the first, second, and third contact elements. The stacking substrate optionally includes separate ground planes and/or power planes for controlled impedance signal traces.
The assembly optionally includes a heat spreader disposed between individual ones of each module, preferably in contact with a non-terminal side of each semiconductor device, which serves as a heat sink and heat exchanger for waste heat generated by the device during operation. The heat spreaders preferably include cooling fins suitable for cooling, if desired, by passive or forced air convection. In the alternative, or in addition, the assembly additionally includes a fluid channel which may be used to direct a cooling fluid, such as ambient air, over or around the semiconductor device in each module.
A more complete understanding of the stacked semiconductor device assembly with microelectronic spring contacts, and components thereof, will be afforded to those skilled in the art, as well as a realization of additional advantages and objects thereof, by a consideration of the following detailed description of the preferred embodiment. Reference will be made to the appended sheets of drawings which will first be described briefly.